1. Field of the Invention
The present invention relates to an acceleration responsive control system and method for an internal combustion engine. It discriminates between a non-accelerating mode and an accelerating mode of the engine and controls the engine in accordance with the determined operational status.
2. Description of Related Art
In an internal combustion engine (such as an outboard boat engine that needs to produce large torques in a very low speed range), ignition timing must be advanced in accordance with throttle demand for acceleration in order to produce a required torque level. A conventional internal combustion engine of this type typically employs: (a) a link operatively connected to a throttle valve so as to advance ignition timing in accordance with throttle valve operation, or (b) an electronic control with a throttle angle sensor detecting throttle valve angle and a microcomputer for processing the sensor signal to control ignition timing.
However, if such a throttle angle sensor or complicated link mechanism is utilized, the construction of the entire control system becomes considerably complicated and costly. In particular, the link mechanism requires a complicated adjustment function and thus causes various drawbacks (e.g., complicated maintenance).
If ignition timing is conventionally controlled in accordance with only throttle valve angle, ignition control is performed in a single manner regardless of whether the engine is accelerating or decelerating or in steady state, despite the fact that different ignition timings are required for accelerating and non-accelerating modes. Therefore, if such an ignition control is based on, for example, an assumed accelerating mode, it fails to perform optimal ignition control during a non-accelerating mode.
Japanese patent application laid-open publication No. SHO 63-205462 discloses a control that converts the amount of change in engine speed over a predetermined crank angle into the corresponding change in engine speed over a unit time to determine whether the engine is accelerating or decelerating and corrects the ignition timing accordingly.
However, since this control uses instantaneous change in engine speed over a predetermined small crank angle for determining engine operational status, the control appropriately performs when instantaneous engine speed fluctuation or vehicle vibration is substantially prevented, but may well provide the wrong determination when instantaneous engine speed fluctuations are great, for example, during idling.